The finite geometric series formula is a(1-rⁿ)/(1-r). In this video, Sal gives a pretty neat justification as to why the formula works. Watch the next lesson: https://www.khanacademy.org/math/math-1-2-3/math3/math3-series/math3-geo-series-app/v/geometric-series-word-problem?utm_source=YT&utm_medium=Desc&utm_campaign=highschoolmath Missed the previous lesson? https://www.khanacademy.org/math/math-1-2-3/math3/math3-series/math3-geo-series/v/three-examples-of-evaluating-finite-geometric-series?utm_source=YT&utm_medium=Desc&utm_campaign=highschoolmath High School Math on Khan Academy: Did you realize that the word "algebra" comes from Arabic (just like "algorithm" and "al jazeera" and "Aladdin")? And what is so great about algebra anyway? This tutorial doesn't explore algebra so much as it introduces the history and ideas that underpin it. About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything. ... https://www.youtube.com/watch?v=Cf0-6ngH2gs Note: All Khan Academy content is available for free at (www.khanacademy.org)

Watch Sal work through a harder within-sentence punctuation question from the SAT Writing and Language Test. Watch the next lesson: https://www.khanacademy.org/test-prep/sat/sat-reading-writing-practice/new-sat-writing-grammar/v/possessives-basic Missed the previous lesson? https://www.khanacademy.org/test-prep/sat/sat-reading-writing-practice/new-sat-writing-grammar/v/within-sentence-punctuation-harder ... https://www.youtube.com/watch?v=GSy4XwV67iM Note: All Khan Academy content is available for free at (www.khanacademy.org)

Watch Sal work through a basic Percents problem. Watch the next lesson: https://www.khanacademy.org/test-prep/new-sat/new-sat-math/new-sat-problem-solving-data-analysis/v/sat-math-q2-harder?utm_source=YT&utm_medium=Desc&utm_campaign=NewSAT Missed the previous lesson? https://www.khanacademy.org/test-prep/new-sat/new-sat-math/new-sat-problem-solving-data-analysis/v/sat-math-q1-harder?utm_source=YT&utm_medium=Desc&utm_campaign=NewSAT New SAT (starting March 2016) on Khan Academy: Practice all of the skills you’ll need for the new SAT. We also have four official practice exams from College Board. The October 2015 PSAT is in the style of the new SAT. About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content. ... https://www.youtube.com/watch?v=aZl9csOSvQU Note: All Khan Academy content is available for free at (www.khanacademy.org)

U07_L3_T1_we2 Simplifying Radical Expressions 2 Content provided by TheNROCproject.org - (c) Monterey Institute for Technology and Education ... https://www.youtube.com/watch?v=F5iMsjwFLX8 Note: All Khan Academy content is available for free at (www.khanacademy.org)